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Subject: Re: [PATCH v2 1/3] mtd: spinand: Add #define-s for page-read ops with
 three-byte addresses
To:     Schrempf Frieder <frieder.schrempf@kontron.de>,
        Marek Vasut <marek.vasut@gmail.com>,
        Boris Brezillon <bbrezillon@kernel.org>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>
Cc:     "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20190514215315.19228-1-lede@allycomm.com>
 <20190514215315.19228-2-lede@allycomm.com>
 <355bcf8d-bce6-1b82-0f57-539c8d9b6cac@gmail.com>
 <efcbdd61-d60e-a5d1-9f91-f8f747fadecf@kontron.de>
From:   Jeff Kletsky <lede@allycomm.com>
Message-ID: <d62d64a9-c7c3-3b0b-a3ba-71ab2a4f61e4@allycomm.com>
Date:   Sun, 19 May 2019 13:27:58 -0700
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On 5/14/19 11:49 PM, Schrempf Frieder wrote:

> On 15.05.19 08:17, Marek Vasut wrote:
>> On 5/14/19 11:53 PM, Jeff Kletsky wrote:
>>> From: Jeff Kletsky <git-commits@allycomm.com>
>> That #define in $subject is called a macro.
>>
>> Seems this patch adds a lot of almost duplicate code, can it be somehow
>> de-duplicated ?
> We could add another parameter naddr or addrlen to the
> SPINAND_PAGE_READ_FROM_CACHE_XX_OPs and pass the value 2 for all
> existing chips except for GD5F1GQ4UFxxG which needs 3 bytes address length.
>
> This would cause one more argument to each of the macro calls in all
> chip drivers. As long as there are only two flavors (2 and 3 bytes) I'm
> not sure if this really would make things easier and also this is "only"
> preprocessor code.
>
> So anyways, I would be fine with both approaches, Jeff's current one or
> one with another parameter for the address length.
>
> By the way: Jeff, you didn't carry my Reviewed-by tag to v2. So I will
> just reply again to add the tags.
>
>>> The GigaDevice GD5F1GQ4UFxxG SPI NAND utilizes three-byte addresses
>>> for its page-read ops.
>>>
>>> http://www.gigadevice.com/datasheet/gd5f1gq4xfxxg/
>>>
>>> Signed-off-by: Jeff Kletsky <git-commits@allycomm.com>
>>> ---
>>>    include/linux/mtd/spinand.h | 30 ++++++++++++++++++++++++++++++
>>>    1 file changed, 30 insertions(+)
>>>
>>> diff --git a/include/linux/mtd/spinand.h b/include/linux/mtd/spinand.h
>>> index b92e2aa955b6..05fe98eebe27 100644
>>> --- a/include/linux/mtd/spinand.h
>>> +++ b/include/linux/mtd/spinand.h
>>> @@ -68,30 +68,60 @@
>>>    		   SPI_MEM_OP_DUMMY(ndummy, 1),				\
>>>    		   SPI_MEM_OP_DATA_IN(len, buf, 1))
>>>    
>>> +#define SPINAND_PAGE_READ_FROM_CACHE_OP_3A(fast, addr, ndummy, buf, len) \
>>> +	SPI_MEM_OP(SPI_MEM_OP_CMD(fast ? 0x0b : 0x03, 1),		\
>>> +		   SPI_MEM_OP_ADDR(3, addr, 1),				\
>>> +		   SPI_MEM_OP_DUMMY(ndummy, 1),				\
>>> +		   SPI_MEM_OP_DATA_IN(len, buf, 1))
>>> +
>>>    #define SPINAND_PAGE_READ_FROM_CACHE_X2_OP(addr, ndummy, buf, len)	\
>>>    	SPI_MEM_OP(SPI_MEM_OP_CMD(0x3b, 1),				\
>>>    		   SPI_MEM_OP_ADDR(2, addr, 1),				\
>>>    		   SPI_MEM_OP_DUMMY(ndummy, 1),				\
>>>    		   SPI_MEM_OP_DATA_IN(len, buf, 2))
>>>    
>>> [ _3A addition repeated three more times for similar ops ... ]

It's easy enough to change the wording, and will do so on the next revision.

However, it's not clear to me that there is consensus on if the present
set of macros is acceptable/preferred over definition of a set of ones
that accept an additional parameter.

At least from my perspective and as Schrempf Frieder has hinted at,
these macros are syntactic sugar and all result in equivalent C code.

Either should compile to the same run-time size and performance (assuming
reasonably that a construct like `true ? 0x0b : 0x03` is optimized out).

Adding an additional parameter, at least for me, wouldn't improve readability
of the code and is offset by the need to refactor four other files. Even
though it should be a simple/trivial refactor, I do not have any examples
of the four other manufacturers' chips to be able to confirm proper operation.

I'll prepare a reworded set of patches with the present macro structure.

If there is strong feeling for refactoring the macro set, please let me know.


Jeff